Repsol YPF

Heat pumps

A heat pump is a machine that transports heat from an atmosphere with a low temperature to another atmosphere with a higher temperature: if we have a liquid that boils at a low temperature, we can transport the heat absorbed by the liquid when boiling in an atmosphere with a low temperature to the atmosphere that is at a higher temperature.

The main characteristic of heat pumps is that, by means of a four-way valve, the direction of flow of the refrigerant can be reversed and they can be made to work following a refrigeration cycle. The heat pump is then said to reversible.

Heating and refrigeration cycles of a heat pump

• Heating cyle:  This is the normal operating cycle of a heat pump. The refrigerant is compressed and taken to a heat exchanger situated in the room that needs to be heated, where it condenses, releasing heat. The refrigerant, in a liquid state, passes through a lamination valve, which decreases its pressure and therefore also the evaporation temperature. Following this, it passes through an exchanger situated on the outside, where it evaporates, absorbing heat from the outside, and returns to the compressor, beginning a new cycle.     
  
• Refrigeration cycle: This is the cycle followed by a reversible pump when the direction of flow of the refrigerant is reversed. In this case, the refrigerant comes out of the compressor, towards the exchanger situated on the outside, and condenses, releasing heat to the outside. On passing through the lamination valve, its pressure and temperature are reduced and when it reaches the exchanger situated on the inside, it evaporates, absorbing heat from the inside.

• Comparison between electric- and gas-operated heat pumps